One of the most pressing problems in the manufacture of leather is the partial or complete replacement of auxiliary agents, which place a great strain on the waste water systems of factories. This is the case especially with regard to the tanning of fur skins and leather, as well as the defatting and the pretanning of skins smoothed by pickling. In addition to tanning agents, other auxiliary agents, such as solvents, defatting agents, tensides, electrolytes, phosphates, neutralizers, etc., are used in the processes of leather manufacture.